Chemical Energetics

Question 1

Lattice energy

Equation (using NaCl)

Endo/ Exo

Answer 1

The energy change when 1 mole of ionic compound is formed from its gaseous ions

Na+ (g) + Cl- (g) -> NaCl (s)

Exothermic

Question 2

Enthalpy change of formation

Equation (using NaCl)

Endo / Exo

Answer 2

The energy required to form 1 mole of compound from its elements under standard conditions

Na(s) + 1/2 Cl2 (g) -> NaCl (s)

Endo or exo

Question 3

First ionization energy

Equation (using Na)

Endo /Exo

Answer 3

The energy required to remove I mole of electrons from one mole of gaseous atoms to form 1 mole of gaseous ions under standard conditions

Na(g) -> Na+(g) + e-

Endothermic

Question 4

Atomization

Equation (use Na and Cl2)

Endo / Exo

Answer 4

The energy change when 1 mole of gaseous atoms is formed from its elements in its defined physical state under standard conditions

1/2 Cl2 (g) -> Cl (g)
Na (s) -> Na (g)

Endo

Question 5

Bond enthalpy

Equation

Endo / Exo

Answer 5

The energy needed to break 1 mole of covalent bond from its elements/compounds in the gaseous state

H2(g) + Cl2(g) -> 2HCl(g)

Endo

Question 6

Relationship between atomization and bond enthalpy

Answer 6

Atomisation = 1/2 Bond Enthalpy

Question 7

Electron Affinity

Equation for Cl

Endo / Exo

Answer 7

The energy change when 1 mole of atoms or ions in the gaseous state gain 1 mole of electrons to form a negative ion

Cl(g) + e- -> Cl-(g)

1st EA = Exo
2nd EA = Endo

Question 8

Hess Law

Answer 8

If a reaction can take place by more than 1 route, and the initial and final conditions are the same, the total enthalpy change is the same

Question 9

Factors affecting Lattice Enthalpy

Answer 9

1) Size of ion - the larger the size, the less exothermic

2) Charge of ion - the higher the charge, the more exothermic

Question 10

Enthalpy change of Solution

Equation

Endo/Exo

Answer 10

The energy change when 1 mole of solute is dissolved in sufficient water to form aqueous ions

NaCl(s) + an -> Na+ (aq) + Cl- (aq)

Either Endo/ Exo

Question 11

Enthalpy change of Hydration

Equation for Na+

Endo/Exo

Answer 11

Energy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution

Na+(g) + aq -> Na+(aq)

Exo

Question 12

Equation for Enthalpy change of Solution

Answer 12

Enthalpy change of Solution = Hydration - Lattice energy

Question 13

Entropy

Symbol

Unit

Answer 13

The measure of the disorder/arrangement of particles and the kinetic energies of particles in a system

S

JK-1mol-1

Question 14

What increases entropy?

- 4 factors

Answer 14

1) Higher temp - more KE and move faster
2) Change of State - solid < liquid < gas
3) Increase in number of particles
4) Mixing of particles

Question 15

Spontaneity of Entropy Change

- What do + and - indicate?

Answer 15

Positive = Spontaneous 
Negative = Non-spontaneous

Question 16

Equation for Entropy of a System

Answer 16

Entropy of System =

Entropy Products - Entropy Reactants

Question 17

Equation for Entropy of Surroundings

Answer 17

Entropy of Surroundings =

-delta H reaction / temperature

Delta H x1000 to change from kJ to J
Temp in K

Question 18

Equation for Entropy Total

Answer 18

Entropy Total =

Entropy System + Entropy Surroundings

Question 19

Gibbs Free Energy used to determine what?

+ and - mean what?

Answer 19

To determine spontaneity of a reaction

\+ = non spontaneous
- = spontaneous

Question 20

When does the reaction become spontaneous for Gibbs Free Energy?

Answer 20

When delta G = 0, it becomes spontaneous

Question 21

2 equations for Gibbs Free Energy

Answer 21

Delta G = Delta H - Temperature(Delta S system)

G = G products - G reactants